Video on demand is a service offered by a server which allows a user of a terminal to watch a film of his choice from amongst a predetermined list. More precisely, for this purpose, the terminal sends a request to the server indicating the chosen film, and he receives in return a digital data stream relating to this film. In this context, the terminal may wish to modify the speed of display of the film during the reception, by increasing this speed for an accelerated viewing or by reducing it for a viewing in slowed down mode, or reversing the direction of reading for a fast return. The modification of this speed is based on the management of modes referred to as ‘trick modes’.
The document US20060037057 provides a management procedure for these trick modes in the context of reception of a video. In this document, when a terminal wishes to increase the speed of display of the video, it sends a request of the GET type according to the HTTP protocol which comprises physical addresses of the images to be displayed in the accelerated mode. Then, the server transmits to the terminal the digital data corresponding to these physical addresses.
This management of the trick modes is based on the physical addresses of the images in the video and, for this reason, notably allows the partial selection of the images of the video to be displayed. When an increase in the speed of display is requested, the user of the terminal views only a part of the content of the video, and in this sense, the speed of display is increased with respect to a duration of display of the video under the same network conditions without the trick mode.
However, in certain cases, the duration of display might not correspond to the acceleration requested via the trick mode with respect to the nominal duration of the video. For example, if an acceleration of four times the speed of display for the whole duration of the video is requested, it is possible for the total duration of display of the video in this accelerated mode to be much longer than the nominal duration of the video (in other words at the speed of 24 or 25 images per second) divided by four.
Thus, in the context of the document US20060037057, the viewing four times faster of a video can take substantially longer than a quarter of the duration of the video under certain network conditions, notably when the data transmission rate over the network is very low.